Radio beacon system



E. l. ANDERSON 2,403,429

RADIO BEACON SYSTEM July 9, 1946.

Filed Nov. 2, 1942 3 Sheets-Sheet 2 JUUL 54w roar/1 W I v Cad/V753 L mm J9 GENE/P147018 4/ PECE/l/EB 1 Fg F5714 lynx.

Zmventor Earl Zflmkmm 6&2. M

(Ittorneg Patented July 9, 1946 asmo BEACON srs'ram Earl-I. Anderson, Manhasset, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 2, 1942, Serial No. scam This invention relates to a course and position determining system employing radio beacons, and receiving apparatus carried by a. mobile craft or vehicle whose position is to be ascertained.

Radiogoniometric systems, in which bearings of two or more fixed stations with respect to a craft are used to determine its position by tri angulation, are subject to various well known sources of error. Under certain conditions of abnormal-wave polarization and high noise level such systems are useless. These difllculties often occur at a time when it is impossible to obtain a fix by astronomical or other means and depend- -able radio location is most required.

It is proposed to use two or more fixed transmitt'ers sending timed impulses to determine the relative time required for a' pulse from each of the transmitters to travel between theilxed stations and the position to be determined. Since the velocity of propagation of radio waves is invariable, the time is in each case an accurate measure of the distance. Although reflections and deviations of the wave may occur, as long as any component of the radio energy travels over the direct path, it will arrive first at the receiver. The position may be ascertained in terms of the relative time of arrival of pulses from the fixed s a ons.

It is an object of this invention to provide method of and means for indicating automatically the position of a mobile. craft with reference to a given course and destination.

Other and incidental objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawings, of which Fig. 1 represents the course and destination of an airplane, for example, with reference to fixed ground stations.

Figs. 2 and 3 illustrate pulses received from the ground stations at a receiver on the airplane.

' Fig. 4 is a, schematic circuit diagram of a system for providing indication of the position of a receiver with respect to three transmitters,

Fig. 5 is a schematic diagram of a modified 7 Claims- (Cl. 250-11) 2 Figs. 8 and 8-11 show a modification oi? the system of Fig. 5,

Figs. 9, 10, 11 and 12 show various types of indications which may be produced by the sys 5 tem of Fig.8, Fig. 13 illustrates another modification of the system of Fig. 5 and Figs. 14, 15, 16, 1'7 and 18 show typical indications obtainedwith the system of Fig. .13.

Referring to Fig. 1, assume that transmitters are located at X and Y, and it is desired to 201- low a course along the line AB, perpendicular to and biseoting the linebetween the transmitters X and Y. Discrete pulses of high frequency en ergy are periodically emitted simultaneously by transmitters X and Y. These pulses are transmitted on different frequencies and picked up by separate receivers at the mobile station. The outputs of the two receivers-are applied. to a 20 multigrid tube arranged to produce output current only when the input pulses coincide. This output current is applied to a peak indicatin device.

As long as the mobile station follows the course AB the arrival of the pulses from the two stations will coincide, producing an output pulse lilsethat 3 shown in Fig. 2. When the mobile station is oil the course AB, theoutput pulse will decrease in I time 01 arrival exceeds the duration time of one pulse. This is illustrated. in Fig. 3.

' In order to indicate the arrival at a destinae ticn, a third transmitter Z, may be provided anywhere along the course AB and arranged to send out pulses like those from x and Y, but with I a slight delay, so that when all three pulses coincide at the receivers, the craft is at its destination, indicated by the point P in Fig. l. I

- Referring to Fig. d, an indicator system is 40 shown, com-prisms receivers X, Y, and Z an ranged to respond to transmitters K, Y and 2; respectively. Receivers X and if are connected .to two control grids oi a multigrld tube 6. The control grids are both normally biased to cut oil? by means of a voltage from e110. source (not shown) applied between the cathode of the tube I and the grid leaks 3 and 5.

The plate circuitof the tube l includes a load resistor 'l coupled through a blocking condenser 60 8- to' a peak indicator comprising ameter ii shunted by a rectifier it.

A second multi rid tube l5, biased like the tube 1, has. one control grid connected through a phase inverter it to the plate circuit of th tube I and the other connected to the receiver Z. A

aaoaeao 3 peak indicator including a meter l7 and rectifier l9 is'connected to the plate circuit of the tube in.

In operation, the plate current. pulses of the tube l are directly related in magnitude to the time of overlapping ofth pulses received by the receivers X and Y,'. Thus the meter II will show a maximum deflection when the craft is on course, and a decrease upondeparture from the course. Similarly the deflection of the meter ll will increase as the destination is approached, attaining a maximum value when it is reached and dropping 01! again if it is passed.

Fig. shows a system for producing course and destination .indications on the screen of a cathode ray tube. A saw-tooth generator 2!, which may be a blocking oscillator, for example, of the type described in U. S. Pat. 2,101,520 to 66, and the cathode is coupled to the grid of Tolson et al., is synchronized with alternate pulses in the output of the receiver x'. The output of the generator II is applied-to the horizontal deflection circuit of a cathode ray tube 23, and the outputs of the three receivers X, Y, and Z are applied together to the vertical deflection circuit of the cathode ray tube.-

Alternate pulses in the output of the receiver X will produce a deflection at the center of the cathode ray trace 21 (Fig. 6). The pulses from receivers X and Z will produce deflections 29 and 3| which are displaced from, the center as functions of time. When the deflection caused by the receiver Y coincide with the central deflection 25, the receiver station is on course. when all th ee deflections coincide, the destination has been reached. In this application the shape of the pulses is not critical except that they should be as short as possible tot maximum accuracy. Fig. '7 shows a portion of the trace on the cathode ray tube when the receiver station is slightly oi! course and near the destination. There is no easy way to distinguish which deflection corresponds to the course indication and which to the destination indication. This information must be determined by going first one way and then the other, long enough to move the deflections a perceptible distance along the trace. If all three pulses arrive at the same time it is impossible to tellif one, two. or three pulses are present, even if the amplitudes are diflerent, since only one composite pulse results.

Fig. 8 shows a system for displaying the received pulse during separate scans of the cathode ray beam, retaining the form of each pulse, even though they arrive coincidentally. The receiver x synchronizes a saw-tooth generator H on alternate pulses, as in the system of Fig. 5. The oscillator output goes to the horizontal deflection circuit of the cathode ray tube 23, and

also to a counter circuit 83, which may be of the type described in British Pat. 471,731, of Dec. 4, 1935, to E. L. C. White adjusted for 3 to 1 frequency division to produce the stepped wave 35. The counter output is applied to one side of the vertical deflection circuit of the cathode ray tube 23 and to a keying pulse generator 3?. The keying pulse generator provides three square wave outputs, 38, ll and 43, each corresponding in time with one of the steps of the wave 35.

These outputs are. applied to key the amplifiers The plate circuit is coupled to the grid of a tube,

another tube 42. The plate of the tube 42 is coupled to the grid of a tube 14, andthe cathode of the tube is is coupled to the cathode of the tube M.

The tube 36 provides a, duplicate of the wave 35 (Fig. 8) in its cathode circuit, and a similar but inverted wave in its plate circuit. The tubes 68 and 12 are arranged to operate as peak "amplifiers, clipping the highest step of the stepped wave in each case. Thus the output at the cathode of the tube 40 is the wave 43 of Fig. 8 and that at the cathode of the tube 42 is the wave 39. The outputs at the plates of these tubes are similar to, but inverted with respect to the cathode outputs. The wave II is provided by applying both of the waves 39 ad 43 to the tube as so as to provide cutofl bias. Thus the tube will conduct when both voltages 39 and are oil.

The amplifiers as, 61 and 49 may comprise multigrid' tubes and circuits like those shown in Fig. 4. or may be any other type'of amplifier arranged to be normally cut oil and made operative by arrival of a keying impulse. Receivers X, Y and Z are connected to the inputs of ampliflex-s d5, 57 and it respectively. The amplifier outputs are applied to the vertical deflecting circuit of the tube 215.

' The operation oi. the system is as follows: Each alternate pulse from the receiver X causes the cathode ray to trace one horizontabsweep. with its center coinciding in time with theintermediate pulse from recevier X. The counter lit is operated by each saw-tooth wavaso that each step in its output has a duration equal amplifiers Alli, ti and [.59 are sequentially keyed to operate successively, each for a period equal to twice the pulse repetition time. The wave-1 may be applied to the vertical deflection circuit, as shown, to cause successiv horizontal traces to appear at different levels. During successive traces the impulses from receivers 'X', Y and Z are successively indicated on the screen, resulting in an indication like that shown in Fig. 10. If the voltage is not used, the patterns will he like that shown in Fig. 9, or if the outputs of the different channels are unequal, like Fig. 11. An indication like that shown in Fig. 12 may he obtained by reversing the polarity. of one of the amplifier outputs, bymeans oi" aphase inverter stage 66, for example. The two lower pulse may be used to indicate course and the upper pulse used to show the destination.

Fig. 13 shows a system for providing indications like those shown in Figs. 14, 15; 16,.17 and- 18, which can be more readily interpreted than those given by the above described systems. Fig. 14. shows the indication when the craft'is on course. Figs. 15 and 16 are ofl-course indications. to the right and to the left respectively. 17 indicates the mobile station is on course and nearits destination. Fig. 18 is the indication-of arrival at the destination. Thus the imageon the cathode ray screen simulates a map showing the positions of the craft and its destination. and the course to he followed. j

The indicator system (Fig. 13) comprises a sawtooth wave generator a! synchronized on alternate pulses in the output of the receiver X, as in the systems of Figs. 5 and 8. A pair of keying:

Fig.

amplifiers It and IS, which may be multigrid tubes biased like the tubes i and ii of Fig. 4, are each connected to produce output only when signals are applied to both control grids. The output of the saw-tooth generator 2| is applied to 'corre sponding control circuits of the amplifiers 53 and II and to a two to one' counter circuit 33. The output of the counter 33 is applied directly to the other of the control inputs of the amplifier 53 and through a phase inverter ii to the corresponding circuit of the amplifler $5. The output circuits: of the amplifiers BI and 55 are connectedto the vertical and horizontal deflection circuits respectively of a cathode ray tube 23. The output of the counter II is also connected through a phase inverter 50 to the vertical deflection-circuit of the tube 23, and the output of the phase inverter ii is similarly connected through a phase inverter 51 to the horizontal deflection circuit. The receivers Y and z' are connected throughswitches 6i and II to the vertical and hprizontal deflection circuits respectively 01 the tube '23. Switches II and 63 may also be operated to connect the receiver X instead of receivers Y and Z to the deflection circuits.

The amplifiers .53 and 85 are keyed alternately by the output currents 85 and 81 of the counter 33 and phase inverter 5i, respectively to produce alternate horizontal and vertical sweeps of the cathode-ray beam of the tube 23. The outputs It and H oi the amplifiers 53 and 55, if applied alone to the respective deflection circuits of the I claim as my invention: 4

' 1. A system for indicating a position in response to arrival at said position of pulses transmitted in predetermined time relationship from a plurality of spaced transmitters, comprising receiver means, a cathode ray tube, means for initiating a sweep ofthe beam 01' said cathode ray tube in response to the arrival of each alternate pulse fromone oi the transmitters, and means for deflecting said beam transversely of said. sweep in response to the arrival of pulses from each of the other transmitters.

2. A system for indicating position in response to the relative timings of a plurality of trains oiperiodic impulses comprising a radio receiver arranged to respond to one of said trains, a sawtooth wave generator controlled by the output of said receiver to operate at a frequency one half of the impulse repetition frequency of said train, other radio receivers arranged to respond respec- .tively to others of said trains, and a cathode ray tube provided with a horizontal deflection circult connected to said saw-tooth wave generator and a vertical deflection circuit connected to said other receivers.

3. A system for indicating position in response to the relative timings of a plurality of impulse tube 23, would produce alternate vertical and horizontal sweeps from the undeflected spot position, at the approximate center of the screen. The traces would intersect at their ends at this point. The phase inverters-S1 and 59 addsquare wave components derived from the counter output to the outputs II and 88 of the keying amphflers, providing resultant voltages I3 and 15 respectively. This is done to make the vertical and horizontal cathode ray traces cross at their centers by shifting the axis of the sawtooth waves 68 and H from zero voltage to one-half the peak voltage.

Alternate pulses, in the output 01 the receiver X' control the initiation of each sweep, which requires a time equal twice the pulse repetition period. An impulsereceived on receiver Y during the horizontal sweep period produces a vertical deflectionf'if this coincides with an impulse from receiver X21 the deflection occurs at trains comprising a radio receiver arranged'to respond to one of said trains, a saw-tooth wave generator controlled by the output of said receiver and arranged to synchronize with alternate impulses of said-train, a frequency divider connected to said saw-tooth wave generator and arranged to produce in response thereto a stepped wave; each step thereof corresponding in duration to one cycle of operation ofsaid saw-tooth wave generator, square wave generators arranged to operate selectively in response to the occurrence of respective levels of said stepped wave, other radio receivers arrangcd'to respond respectively to others of said impulse trains, amplifiers connected to the outputs of the-receivers and each arranged to be controlled by one of said square the center of the horizontal sweep. A pulse from receiver Z during the vertical sweep produces a horizontal deflection, above or below the center according to whether it is later or earlier than the pulse from x'. When all three pulses coinside in arrival, the deflections both occur at the intersection of the sweeps.

The switches ti and $3 are provided so that the output of the receiver x' may be applied to either of the deflection circuits to enable observation of the amount oi square wave component added to each of the deflection saw-tooth voltages, for the purpose of adjustment.

Thus the inventiomhas been described as a course and destination indication system for mobile craft. Trains of suitably timed impulses are transmitted at equal repetitionperiods from a plurality of listed stations and received at the mobile station. Coincidence of two of the pulse trains at the receiver station occurs when the craft is on course, and coincidence of all three v occurs at the destination. Several arrangements for providing visual indications in response to the received pulses are illustrated.

wave generators, vands. cathode ray tube, with a first deflection circuit connected to said sawtooth wave generator and a second deflection circuit connected to'sald frequency divider and to allof said amplifiers.

4. A system for determining position in response to the relative timings of a plurality oi impulse trains comprising a plurality of radio receivers, each arranged to respond to one of said trains, a cathode ray tube, means for deflecting the beam of said cathode ray tube in alternate sweeps at right angles to each other,, said means being arranged to respond to the out-.

put of one of said receivers so that each of said sweeps has a duration of twice the pulse repetition period of said output, and means for deforming each of said'sweeps in response to impulses in the output of a corresponding one of the others of said receivers.

5. A system for indicating a position in response to the relative timings of a plurality of 'trains of periodic impulses comprising a radio re-v ceiver arranged to respond to one of said trains,

a saw-tooth wave generator connected to said receiver and arranged to initiate a cycle in response to the arrival of each alternate impulse of said train at receiver. a cathode raytube with one deflection circuit connected to said saw-tooth wave generatorwhereby the beam of said cathode ray tube produces a linear'trace on the screen thereof, other radio receivers arranged to respond respectively to others of said trains, and connections from the output circuits of all of said other receivers and another deflection circuit of said cathode ray tube whereby said linear trace is deformed at points along its length related in their positions to the relative timing of said impulse trains. V

6. The method of indicating on a cathode ray tube the position or a station in response to arrival at said station of a plurality of trains of timed pulses, comprising the steps of initiatin a sweep of the beam of said cathode ray tube in response to the arrival of each alternate pulse of one of said pulse trains. and deflecting said 7. The method of indicating position on a cathode ray tube in response to the relative timings of a plurality oi trains comprising the stem of deflecting the beam or said cathode ray tube in alternate sweeps at right angles to each other in response to the successive alternate pulses of one of said trains, and deforming each of said sweeps respectively in response to the pulses of corresponding other trains.

EARL I. ANDERSON. 

